This invention relates to a two-cycle internal combustion and particularly a six cylinder V-engine with cylinder banks for mounting as a part of an outboard motor.
A V-engine employs a pair of cylinder banks angularly oriented with respect to a common crankcase. V-engines generally employ a centrally located exhaust manifold chamber with a central wall providing individual exhaust chambers for each bank. This limits the space and may require special machining and the like because of the restricted entrance to the individual chamber for each cylinder bank.
In outboard motors, the engine is mounted to the top of the driveshaft housing and enclosed within a decorative sound deadening cowl.
The V-shaped engine does permit lowering of the profile of the engine. However, the conventional ninety degree V-engine significantly increases the width of the engine. Increasing the number of cylinders in each bank tends to create an OMC overall bulky appearance of the powerhead.
The engines for outboard motor units and the like are of the two-cycle construction with pressurized crankcase charging of the cylinders. The charge is introduced in either of two distinct methods known respectively as cross charging and scavenging and as loop charging and scavenging. Conventional cross charging and scavenging permits simplified manufacturing and minimizing of cost. In such systems, a deflector piston is employed to properly expose the exhaust port means and the input port means, which are located on opposite sides of the cylinder. The input charge, which may be a fuel-air charge or only air in fuel injection systems, is derived from the pressurized crankcase and moves across the piston and is then deflected upward to scavenge the exhaust gases while introducing the new charge. Althrough simple and relatively inexpensive, the system does not provide a highly efficient and effective scavinging and introduction of the new charge.
Loop scavenging is generally more efficient and thus produces a greater power output per cubic inch of piston displacement with a smaller fuel usage per horsepower per hour consumption when compared to cross scavenged engines. In loop scavenging, a pair of side input ports oppositely located in the cylinder directs the charges toward the rear of the cylinder and with a finger port develops a loop path through the cylinder with a wave moving from the back of the cylinder up the combustion chamber then back down to the exhaust port on the opposite side of the cylinder. Thus, the incoming charges meet with each other and with the upward charge from the finger port adjacent to back wall of the cylinder sweep upwardly across the back of the cylinder and then over and downwardly in a distinct loop to the exhaust port. This develops a velocity pattern over the face of the piston which is a maximum at the back wall to a negative pressure created at the exhaust port. Although more efficient, the opposed dual input porting increases the overall height of the cylinder banks and thus further complicates the design of a compact, aesthetically pleasing powerhead for an outboard motor. This is, of course, particularly true in V-engines where it is generally desirable to minimize the height because of the increased width. A loop scavenging porting is also somewhat more complicated and costly and maximum efficiency is desirable to compensate therefore. The loop scavenger system is, therefore, desirable for providing higher specific power levels, lower fuel consumption, and greater reliability particularly with the design simplicity of this invention as presently set forth.
Further, V-engines are generally tuned with individual exhaust chambers cast into the block. The exhaust passageway openings are formed after casting and, because of the restricted size of the exhaust chamber, generally require special machining with a resultant expense.
Although V-engines do, therefore, have advantages for outboard motors and the like, many disadvantages have existed which have discouraged their implementation and use by certain manufacturers.